2. Overview Lecture 2 Trapping antiprotons Antihydrogen ATHENA and ATRAP
Making antihydrogen
Future developments
Applications PET
Antiproton therapy?
Rocket propulsion??

3. The first nine antihydrogen atoms at CERN (1996)

4. How were the 9 antihydrogen atoms made at LEAR ?
Annihilation of 9 anti-atoms ~ 2 nJ ~ Lifting a mosquito by 1 µm

5. Press reactions (of course)
“Liberation” (France)

6. Two questions to keep you awake
1. With present techniques, what would be the price and delivery time for an 0.5 g anti-hydrogen bomb?
The Vatican ?
2. How much antimatter propellant would you need to accelerate a 10-ton spacecraft to 95 % of the speed of light (assuming 100% efficiency)

7. III. TRAPPING ANTIPARTICLES

8. RF trap (“Paul trap”) - / + + / -
A radio-frequency current on the electrodes maintains an alternating electric field that confines charged particles in a small space.
+ / -
- / +

9. Magnetic traps
Typical voltages: V
For trapping:
~ several kV

10. Special case: Penning trap
Electrodes with hyperbolic shape harmonic forces: Er ~ r, Ez ~ z
precise oscillation frequencies !

11. The inertial mass of antiprotons (PS 196, LEAR)
Moving antiprotons induce currents in trap wall
The ‘sound of antiprotons’ - at 89.3 MHz (cyclotron frequency)
Compare frequency of antiproton and negative hydrogen ions
G. Gabrielse
Agreement to a precision of 9 x 10-11

12. Reminder: Antiproton Production
Extraction from AD to experiments: 5.3 MeV (~ 0.1 c), 3·107

13. Trapping antiprotons

14. Trap for antiproton capture and storage

15. IV. ANTIHYDROGEN

16. The race for cold antihydrogen
ATHENA and ATRAP - Experiments (Start 2000)
Find a way to make cold antihydrogen (done)
Trap and cool antihydrogen
Precision measurements
ATRAP
ATHENA

17. Antihydrogen = Hydrogen ??
2S level is metastable (T ~ 120 ms)
Two photon laser-spectroscopy (1S-2S energy difference)
very narrow line width = high precision: Δν/ν ~ 10-15
Long observation time - need trapped (anti)atoms

18. Antihydrogen milestones
p- and e+ in mixing trap (cooling)
Antihydrogen formation AD
p- Production (GeV)
Deceleration (MeV)
Na-22
e+ Production (MeV)
Moderation
Accumulation (eV)
108 e+
104 p-
Detection of annihilation
Trapping (keV)
Cooling (meV)

19. Overview - ATHENA / AD-1

20. ATHENA Experiment

21. Positron Accumulation using Buffer Gas
100 million positrons accumulated in 2 min

22. Recombination
*D.S. Hall, G. Gabrielse, Phys. Rev. Lett. 77, 1962 (1996)

23. Antihydrogen Detection
Charged particles
2 layers of Si microstrip detectors
511 keV gammas
192 CsI crystals
Inner radius 4 cm, thickness ~ 3 cm
70% solid angle coverage
Operates at 3 Tesla, 140 Kelvin
(C. Regenfus et al., NIM A501, 65 (2003))
Event analysis:
Reconstruct vertex from tracks of charged particles
Identify pairs of 511 keV γ-rays in time coincidence
Measure opening angle between the two γ -rays

24. Antihydrogen - The Movie

25. Antihydrogen Detector

26. First observation of cold antihydrogen
Opening Angle Distribution
Peak from back-to-back 511 keV photon pairs
Test: peak disappears when positrons are ‘heated’ (RF)
Correcting for detection efficiency: > 100,000 anti-atoms

27. Rate of antihydrogen production quite high
Initially > 100 Hz

28. Meanwhile: AD-2 (ATRAP)
Different recombination and detection scheme

29. ATRAP - Recombination scheme1 2 3 4 5 6 1
Cs atoms are excited to n~50 2
Cs* atoms collide with positron cloud 3
Formation of excited positronium 4
Ps* collides with cold antiprotons 5
Antihydrogen formation (n ~ 45) 6
Antihydrogen detection by ionisation
Advantage: Positron attached to ‘resting’ (=cold) antiproton
Disadvantage: Low rate (14 antihydrogen atoms detected)

30. ATRAP: Antihydrogen detection by ionisation
Only works for antihydrogen in high-n states (n>35) moving along magnetic axis
Field ionization - ‘rip’ positron off, antiproton left and detected by annihilation

31. Present state of the art
Number of produced antihydrogen atoms Energy
1996: 9 (PS210, CERN) 2 GeV
1998: 60 (Fermilab) 3 GeV
2002: > 1,000,000 (AD) eV
Antihydrogen production works
What about trapping?

32. Next step: Trapping antihydrogen
FUTURE DEVELOPMENTS
Next step: Trapping antihydrogen

33. How to trap antihydrogen
How to trap (neutral) antihydrogen?
1) magnetic moment (~ μe+) - ATRAP/ALPHA approach
2) induced electric dipole moment (Stark deceleration) ?
3) Formation of positive antihydrogen ions (additional e+) ??

34. Example: Sextupole magnet
Magnetic bottles ?
Example: Sextupole magnet
Low field seeking atoms (50%) at r=0
BUT: Very shallow potential (~ 0.07 meV/T)
Realistic ΔB ~ T ➪ E < 0.02 meV
(reminder: produced antihydrogen has Ekin ~ meV)
Trap antihydrogen from low energy ‘Boltzmann tail’ ?

35. Antihydrogen trapping: Laser cooling ?
121 nm laser needed
Prototype at MPI Munich
… only 50 nW

36. V. APPLICATIONS

37. Applications of antimatter - PET
Insert e+ emitting isotopes (C-11, N-13, O-15, F- 18) into physiologically relevant molecules (O2, glucose, enzymes) and inject into patient.
Reconstruct place of positron annihilation with crystal calorimeter

38. Tumour therapy
Goal: destroy tumour without (too much) harm to healthy tissue
Gammas: exponential decay (peaks at beginning)
Charged particles: Bragg peak (Plateau/Peak better for high Z)
Antiprotons: like protons, but enhanced Bragg peak from annihilation

39. Antiproton Cell Experiment
Biological effectiveness of antiproton annihilation in cells
Additional damage by nuclear fragments of short range
Chinese Hamster Cells

40. Antiproton Cell Experiment
Protons
Antiprotons
Cell survival probability
Equal cell mortality for tumour cells with 1/3 radiation dose (= damage to healthy cells)
Interesting result - now compare with Carbon ion therapy - dedicated facility ???

41. E = mc2 Antiproton bombs ? 20 kt TNT ~ 8 · 1013 J
0.5 g antimatter g matter
0.5 g antimatter = 0.5·10-3 · 9 · 1016 J = 4.5 · 1013 J
Total energy needed (efficiency =10-9 ) : 4.5 · 1022 J
EDF discount price CERN (1 kWh = 3.6 · 106 J = 0.1 € ):
Price ~ 1015 €
Maximum production at CERN ~ 1014 antiprotons / ( year ~ 3 · 107 sec
Delivery time ~ 3 billion years

42. Antimatter driven space engines?
10-ton spacecraft at 0.95 c:
E = γmc2 ~ 10 · 104 kg =
50 tons of antimatter + 50 t of matter
Until somebody finds a clever way around these problems, this will stay fiction:
noch nicht !
The End.